This invention relates to a thin film magnetic head and, in particular, to a thin film magnetic head having a high precision magnetic film pattern. This invention also relates to a method of manufacturing such a thin film magnetic head.
The recording density of a magnetic recording apparatus, such as a magnetic disc apparatus or a VTR, is determined by the product of a width of a recording track and a length of the recording bit. The width of the recording track is determined by the width of the tip section of the magnetic film of the thin film magnetic head used (hereinafter referred to as "the track width"). Therefore, to attain a high recording density with such apparatuses, it is required to make the track width small and, at the same time, to prepare a number of magnetic thin films, which are given as patterns on a substrate formed of an alumina-system material, with high precision in terms of track width.
A typical track width formation technique for a thin film magnetic head is disclosed in JP-A-60-37130.
In accordance with the prior-art method, a thin film magnetic head is prepared by the following processes:
a. Successively formed on the surface of a substrate are a base film, a lower magnetic film, a gap layer (formed, e.g., of alumina (Al.sub.2 O.sub.3)), an insulator layer, a conductor coil arranged within the insulator layer, an upper magnetic film, and an alumina film; PA1 b. A photoresist layer is applied onto the alumina film in such a manner as to form a desired pattern; PA1 c. Using the photoresist layer as a mask, a etching process is performed on the alumina film by a reactive ion beam etching method using CF.sub.4 gas or a carbon fluoride gas such as C.sub.2 F.sub.6 or CHF.sub.3 ; and PA1 d. Using the patterned alumina film as a mask, a pattern of the upper magnetic film is formed by ion beam etching using argon gas. PA1 a. forming, successively on a substrate, a base layer, a lower magnetic film, a gap layer, an insulator layer, and a conductor coil; PA1 b. coating the gap layer and the insulator layer formed with an upper magnetic film; PA1 c. coating the upper magnetic film with a first mask; PA1 d. coating the first mask with a second mask which enables the first mask to be selectively etched; PA1 e. performing etching on the first mask; and PA1 f. performing etching on the upper magnetic film masked by the first mask. PA1 a gas mixture consisting of a hydrocarbon fluoride gas which can be expressed by the following general formula: EQU CnHxFy (where n.gtoreq.1, x+y=2n+2, x&gt;0, y.gtoreq.0, and x.gtoreq.y) and PA1 a hydrocarbon fluoride gas which can be expressed by the following general formula: EQU CnHxFy (where n.gtoreq.1, x+y=2n+2, x.gtoreq.0, y.gtoreq.0, and x&lt;y).
In accordance with this method, a number of thin film magnetic head units are simultaneously formed on a single substrate, and, by severing this substrate, each of the units can be obtained.
In the thin film magnetic head thus obtained, a magnetic circuit is formed by the lower and upper magnetic films, between which the insulator layer and the conductor coil are arranged, with the lower magnetic film, the gap layer, and the upper magnetic film partly extending, in the form of tongue-like extensions, to the exterior, beyond the range of the insulator layer. The extension of these tongues is effected in such a manner that the upper magnetic film is lowered to approach the gap layer on the lower magnetic film, gradually, along the side edge of the insulator layer, which are formed as sloping faces. The writing or reading of data to or from the recording medium is effected through the gap layer between the lower and upper magnetic films in the tongue-like extensions.
The width of the upper magnetic film in its tongue-like extension, i.e., the lateral width of the tip section of the upper magnetic film facing the recording medium at a right angle when used as a magnetic head device, constitutes the track width. To make this track width as small as possible and with high precision (i.e., uniformly) among a large number of thin film magnetic heads produced, it is necessary to enhance the precision in the above process b in terms of the width of the photoresist film, the precision in the process c in terms of the width of the alumina film, and the precision in the process d in terms of the etching performed on the photoresist film. Above all, the precision in the width of the photoresist film and that in the width of the alumina film are significant factors in the determination of the track width.